Master's defense: Robert Garbrecht Larsen

Exploring complex quantum Hall interferometers in high mobility GaAs

Quantum Hall edge states provide a platform for realising electronic interferometers. With these interferometers it is possible to probe the properties of the exotic fractional quantum Hall states, including the fractional charge of the quasiparticle excitations of these states and the fractional braiding statistics that arise from the fractional charge. It can also be used as a direct probe of the possibly non-abelian nature of the quasiparticles, a phenomenon that could provide topologically protected qubits for quantum information processing. We measure a number of electronic Fabry-Perot interferometers realised by gating a high mobility GaAs two dimensional electron gas(2DEG), showing that the measurement techniques are sufficient for interferometry. We show that the action of a helper gate in the quantum point contacts(QPCs) forming the interferometer cavity enable the formation of deep and narrow channels. Top gating the material used is shown to reduce the electron mobility dramatically, but fractional quantum Hall states can still be observed. Finally a simple single layer interferometer is demonstrated to work, showing Coloumb dominated behaviour. Gate voltages are shown to change the edge velocity in the interferometer cavity, pointing to a possible method for achieving coherence in a large interferometer. Future experiments combining all these elements to create an interferometer where the number of encircled quasiparticles can be controlled are proposed.